Production of elongated extrusions composed of titanium base metal

ABSTRACT

Elongated extrusions of titanium base metal are produced from billets in the form of coils of titanium base metal. In such a coil, the rolling direction of the sheet and the axis of the convolutions of the sheet are at right angles to each other. It is believed that striated roughness of the resulting extrusion is minimized because grain elongation in the rolling direction and grain elongation in the extruding (axial) direction are such that strain hardening is neutralized.

United States Patent [7 21 Inventor Robert F Packard [56] References Cited 1 N Bgoflklme, Mass- UNITED STATES PATENTS [21] P 7 37,108 12/1862 Reeves 29/1s5x [22] Filed Jan. 28, 1969 3,215,512 11/1965 Coad 29/198X [45 1 Patented May 1971 3 371 407 3/1968 Fors th et al 29/194x [73] Assignee Technical Metals, Inc. y

Bm kmn, Ma Primary Examiner-.lohn F. Campbell Assistant Examiner-Victor A. DiPalma AttorneyMorse, Altman and Oates [54] PRODUCTION OF ELONGATED EXTRUSIONS fgg il fi BASE METAL ABSTRACT: Elongated extrusions of titanium base metal are g produced from billets in the form of coils of titanium base [52] US. Cl 29/423, metal. In such a coil, the rolling direction of the sheet and the 29/ l 87, 29/187.5, 29/194, 29/198, 72/253, 72/258 axis of the convolutions of the sheet are at right angles to each [51] Int. Cl B2311 17/00 other. it is believed that striated roughness of the resulting ex- [50] Field of Search 29/423, trusion is minimized because grain elongation in the rolling (inquired), 185, 187, 187.5, 194, 198; 72/253, direction and grain elongation in the extruding (axial) 258, 268, 700 direction are such that strain hardening is neutralized.

EVAOUATE AND SEAL ENDS PRODUCTION OF ELONGATED EXTRUSIONS COMPOSED OF TITANIUM BASE METAL BACKGROUND AND SUMMARY OF THE INVENTION The present invention relates to the metallurgy of titanium and, more particularly, to the production of elongated titanium base extrusions such as tubes and rods. In the past, difficulties have been encountered in the production of elongated titanium base extrusions, which have suffered from undesired surface roughness. This roughness is evident in the form of deep surface grooves or striations, which are undesirable for two reasons. I. They may act as stress-raisers, leading to cracking or splitting during subsequent cold-drawing operations and 2. they usually cannot be completely or satisfactorily ironed out or removed during'such cold-drawing operations.

In consequence, the unusual combination of light weight and high strength, which theoretically is characteristic of titanium base metal, is often difficult to achieve in tubing or rodstock, particularly tubing for modern aircraft and the like.

The primary object of the present invention is the production of smooth, elongated titanium extrusions that are characterized by a grain structure that is more or less symmetrical in at least two dimensions. This grain structure results from the extrusion of a billet in the form'of a coil oftitanium base sheet characterized by grains which are elongated in the rolling direction of the sheet and which are perpendicular to the axis of the billet, i.e. the axis along which the billetis to be extruded. The extrusion process causes final deformation of the grains in a direction perpendicular to the initial rolling direction of elongation, whereby at least two of the dimensions of the grains become approximately equal, strain hardening thereby being reduced to aminimum. In the cases of both tubes and rods, before extrusion, the billet is encapsulated by a tubular casing or shell composed of another metal. This casing is usually evacuated and then sealed. in order to provide optimum atmospheric conditions for extrusion of the titanium billet. In the case of tubing, an axial core is inserted initially in the center of the coil. The inner core andtheouter casing are composed of thesame material. In.the case of tube production, the inner core and the outer casing are removed chemically following the extrusion. In the case of rod production where there is no inner core only the outer casing need be removed chemically.

Other objects of the present invention will in part be obvious and will in part appear hereinafter.

The invention, accordingly, comprises the processes and products involving the components, steps and interrelationships, which are exemplified in the present disclosure. the scope of which will be indicated in the appended claims.

BRIEF DESCRIPTION OF THE DRAWING For a fuller understandingof the nature and objects of the present invention, reference is made to the following detailed description, taken in connection with the accompanying drawings, wherein:

FIG. 1 illustrates the production of a billet in accordance DETAILED DESCRIPTION Generally, the illustrated process of the present invention comprises: i. forming a billet of titanium base metal from a coil of titanium base sheet, enclosing the billet within-acylindrical can of chemically removable metal and evacuating the interior of the can; 2. extruding: the billet atelevated pressure and temperature through a die opening to produce an'elongated extruded form having a removable. metal casing,.and 3. chemically removing the casing to produce the final elongated extruded product, typically a cylindrical tube or rod. In the illustrated embodiment, the coils of titanium base sheet in the billet are wrapped around a central core so that the elongated extruded shape initially has an internal core and an external casing both capable of being dissolved by chemical action which does not affect the titanium" base metal. Typically, the titanium base metal contains at least 50 percent by total weight of titanium, i.e. contains titanium as its characteristic ingredient. Examples of such titanium base metals are of the following compositions: commercially pure titanium; aluminum-6 percent, vanadium-4 percent, titanium remainder; and aluminium-3 percent;- vanadium-2.5 percent; titanium remainder. Preferably, the chemically removable core and casing are composed of a metal having approximately the same stiffness, i.e. bulkmodulus, as titanium, a preferred metal being mild steel. The assemblage is such that the relative thicknesses of the components of the'billet are approximately the same, respectively, as the relative thicknesses of the components of the extruded shape.

With reference to FIG. 1(a), a sheet 20 of titanium base metal is rolled to predetermined thickness between a pair of work rolls 22, 24. By virtue of deformation resulting from the rolling process, the resulting sheet has a microstructure that is characterized by grains 28 that are elongated in the rolling direction. Typically the thickness of sheet 28 ranges between 0.5 to 50'mils. As shown in FIG. 1 (b), sheet 28 is coiled as at 30 about a rod 32, the resulting coil having in excess of two convolutions and preferably from 10 to convolutions. It will be observed that elongated grains 28 extend in direction 34, which is perpendicular to the axis 36 of rod 32. The resultingconvoluted roll is inserted into a tubular can 38, previously sealed'at one end, as shown in FIG. 1 (0). Generally, steel can parts, as shown in FIG. 2, that previously have been vacuum degassed-areutilized. The open end of the resulting assemblage is sealed by welding to one end of tube 38 a first cap 31 and to the-other end of tube 38a second cap 33, with an integral evacuation tube 35. Thereafter, the assemblage is heated to a temperature in excess of 200 F. and then the interior is evacuated to a pressure of at most 10" mm.Hg. Following evacuation, welding tube 35 is pinched off to seal the interior of-tube' 38. The resulting billet constitutes an intermediate product for extrusion in the press now to be described. Generally, the outside diameter of the billet ranges from2 to 6 inches, the thickness of can 38 ranges from 1/32 to 2 inches, and the diameter of core 32 ranges from to 4 inches.

FIG. 3' illustrates an extrusion press 42 within which billet 40 is placed. Extrusion press42 comprises a container 44 that provides an internal cylindrical-cavity 46 for snugly receiving the billet. At the forward end of cavity 46 is a die 48 having an extrusion opening 50 Die 48 is retained and seated against a shoulder 52 in cylinder by a retaining plate 54. Plate 54 is provided with a central opening 56 in alignment with die opening 50. Reciprocable-within cavity 46 is a disc-shaped ram 58. Preferably. the extrusion temperature is in excess l,500 F. and best results are achieved at approximately 1,650 F. The extrusion pressure is sufficiently high to achieve extrusion at the selected temperature. Preferably the diameter of die opening SOranges between and l /1. inch, although larger and smaller diameters are feasible.

The resulting extruded shape is shown in FIG. 4 as preferably ranging from /2 to l A inch in overall outside diameter. This extruded shape is shown as having a mild steel core 60, a titanium tube 62 and a mild steel shell 64, with cross-sectional dimensions in the same ratios to each other as the cross-sectional dimensions of the original billet counterparts. Furthermore, the layers of titanium base metal making up the original coil 30 become fused together during extrusion thereby producing a strong metallurgical bond. Due to this elevated temperature, solid-state bonding under the great pressures of extrusion, the boundary between coil sheet layers generally becomes indistinquishable even at 200x magnification. The resulting. tubing therefore has a solid, fully dense fected by the nitric acid. Preferably, the outside diameter of the resulting tube ranges from /4 to 1 V4 inch and the internal diameter of tube 62 ranges from 3/16 to l /8 inch. This resulting tube is composed of fused convolutions about its axis and is characterized by grains which have approximately equal diameters in the direction parallel to the axis as at 36 and perpendicular to the axis as at 34.

The following nonlimiting examples further illustrate the present invention.

EXAMPLE I A 0.020-inch-thick sheet of titanium base metal, by total weight, composed of aluminium-6 percent, vanadium-4 percent and titanium remainder was the starting material. 20 layers of this sheet material were coiled about a 2-inch mild steel rod the outer diameter of the coil being approximately 3 inches. The partially fabricated billet was then inserted into a l2-inch-long mild steel can having an outside diameter of 4 inches and a thickness of A inch. An end cap with an integral evacuation tube was welded to the open end of the can. The assemblage was heated to about 300 F. and the interior evacuated to mm.Hg. Then the evacuation tube was sealed by pinching off. The resulting billet was inserted into an extrusion press having a cavity slightly larger than the diameter of the billet. Extrusion was effected at a temperature of l,650 F. through a circular die opening V4 inch in diameter. The resulting extruded shape was immersed in nitric acid to remove the mild steel core and mild steel casing in order to leave a titanium base tube having an outside diameter of approximately 36 inch an inside diameter of inch.

EXAMPLE 2 A 0.0l6-inch-thick sheet of titanium base metal, by total weight, composed of aluminium-3 percent, vanadium-2.5 percent remainder titanium was the starting material. 25 coils of this materials where wrapped around a ii-inch mild steel rod. The partially fabricated billet was inserted into a l0-inch'long mild steel can having outside diameter of 3 inches and a thickness of 1 1/16 inch. An end cap with an integral evacuation tube was welded onto the open end of the can. The assemblage was heated to about 300 F. and the interior evacuated to 10" mm.Hg. and then the evacuation tube was pinched off and sealed. The resulting billet was inserted into an extrusion press having a cavity slightly larger than the diameter of the billet. Extrusion was effected at a temperature of 1,650 F. through a circular die opening inch in diameter. The resulting extruded shape was immersed in nitric acid to remove the mild steel core and mild steel casing in order to leave a titanium base tube having an outside diameter of /4 inch and inside diameter of A: inch.

EXAMPLE 3 A 0.025-inch-thick sheet of commercially pure titanium was the starting material. 55 turns of this material were coiled as tightly as possible without an interior core rod. The partially fabricated billet was inserted within a l2-inch-long mild steel can having a diameter of 3 A; inches and a thickness of H16 inch. An end cap with an integral evacuation tube was welded on the open end of the can. The assemblage was heated to about 300 F. and the interior evacuated to l0 mm.Hg. and then the evacuation tube was sealed off by pinching. The resulting billet was inserted into an extrusion press having a cavity slightly larger than the diameter of the billet. Extrusion was effected at temperature of 1,650" F. through a circular die opening 7/ l6 inch in diameter. The resulting extruded shape was immersed in nitric acid to remove the mild steel casing in order to leave a titanium rod having a diameter of approximately inch.

EXAMPLE 4 The process of as Example 3 was repeated except that a solid core rod of commercially pure titanium /&-inch diameter was used to wrap the coil about.

EXAMPLE 5 The process of Example 3 was repeated except that particles, i.e. commercially pure titanium powder, was rammed tightly into the small center axial void.

The present invention thus involves the production of titanium base rods and tubes having smooth surfaces and microstructures characterized by grain shapes that are responsible for an unprecedented lack of striated surface roughness. Since certain changes may be made in the foregoing disclosure without departing from the scope of the present invention, it is intended that all matter described in the foregoing specification and illustrated in the accompanying drawing be interpreted in an illustrative and not in a limiting sense.

lclaim:

l. A process for producing elongated titanium base metal shapes, s aid titanium base metal including titanium as its characteristic ingredient, said process comprising the steps of orienting a sheet of said titanium base metal in its rolling direction so that elongated grains are orientated along a first axis, coiling said sheet about a second axis perpendicular to said first axis to provide a plurality of convolutions about said second axis to form a billet, and extruding said billet through a die opening at a temperature in excess of 1,200 F.

2. A process for producing an elongated titanium base metal shape, said process comprising the steps of orienting a sheet of said titanium base metal with its elongated grains extending along a first axis, coiling said sheet about a second axis perpendicular to said first axis in order to produce a plurality of convolutions thereof about a core, inserting said convolutions and said core into a can; said core and said can being composed of a second metal having a bulk modulus approximately the same as the bulk modulus of said titanium base metal, evacuating said can and sealing said assemblage at opposite ends thereof, extruding said billet through a die opening at the temperature in excess of 1,200 F. and at a pressure sufficient to effect extrusion, thereby producing an elongated shape having a core and a casing, and chemically removing said core and said casing from the extruded-type titanium shape.

3. The process of claim 2 wherein said titanium base metal is substantially pure titanium.

4. The process of claim 2 wherein said titanium base metal is a titanium alloy.

5. The process of claim 2 wherein said titanium base metal is an alloy of aluminum and vanadium.

6. The process of claim 2 wherein said second metal is composed of mild steel.

7. A process of producing elongated titanium base metal shapes, said titanium base metal including titanium as its characteristic ingredient, said process comprising the steps of orienting a sheet of said titanium base metal in its rolling direction so that elongated grains are orientated along a first axis, coiling said sheet about a second axis perpendicular to said first axis to provide a plurality of convolutions about said second axis to form an intermediate billet, enclosing said intermediate billet in a can to form a final billet, and extruding said final billet through a die opening at a temperature in excess of l,200 F.

8. A process for producing an elongated titanium base metal shape, said process comprising the steps of orienting a sheet of said titanium base metal with its elongated grains extending along a first axis, coiling said sheet about a second axis perpendicular to said first axis in order to produce a plurality of convolutions thereof about a core, inserting said convolutions and said core into a can, said core and said can being composed of a second metal having a bulk modulus approximately the same as the bulk modulus of said titanium base metal, evacuating said can and sealing said assemblage at opposite ends thereof to form a completed billet, extruding said billet through a die opening at a temperature inexcess of 1,200 F. and at a pressure sufficient to effect extrusion, thereby producing an elongated shape having a core and a casing, and

chemically removing said core and said casing-from the extruded-type titanium shape, said titanium base metal being an alloy of aluminum and vanadium, said core and said can being composed of mild steel. 

2. A process for producing an elongated titanium base metal shape, said process comprising the steps of orienting a sheet of said titanium base metal with its elongated grains extending along a first axis, coiling said sheet about a second axis perpendicular to said first axis in order to produce a plurality of convolutions thereof about a core, inserting said convolutions and said core into a can, said core and said can being composed of a second metal having a bulk modulus approximately the same as the bulk modulus of said titanium base metal, evacuating said can and sealing said assemblage at opposite ends thereof, extruding said billet through a die opening at the temperature in excess of 1,200* F. and at a pressure sufficient to effect extrusion, thereby producing an elongated shape having a core and a casing, and chemically removing said core and said casing from the extruded-type titanium shape.
 3. The process of claim 2 wherein said titanium base metal is substantially pure titanium.
 4. The process of claim 2 wherein said titanium base metal is a titanium alloy.
 5. The process of claim 2 wherein said titanium base metal is an alloy of aluminum and vanadium.
 6. The process of claim 2 wherein said second metal is composed of mild steel.
 7. A process of producing elongated titanium base metal shapes, said titanium base metal including titanium as its characteristic ingredient, said process comprising the steps of orienting a sheet of said titanium base metal in its rolling direction so that elongated grains are orientated along a first axis, coiling said sheet about a second axis perpendicular to said first axis to provide a plurality of convolutions about said second axis to form an intermediate billet, enclosing said intermediate billet in a can to form a final billet, and extruding said final billet through a die opening at a temperature in excess of 1,200* F.
 8. A process for producing an elongated titanium base metal shape, said process comprising the steps of orienting a sheet of said titanium base metal with its elongated grains extending along a first axis, coiling said sheet about a second axis perpendicular to said first axis in order to produce a plurality of convolutions thereof about a core, inserting said convolutions and said core into a can, said core and said can being composed of a second metal having a bulk modulus approximately the same as the bulk modulus of said titanium base metal, evacuating said can and sealing said assemblage at opposite ends thereof to form a completed billet, extruding said billet through a die opening at a temperature in excess of 1,200* F. and at a pressure sufficient to effect extrusion, thereby producing an elongated shape having a core and a casing, and chemically removing said core and said casing from the extruded-type titanium shape, said titanium base metal being an alloy of aluminum and vanadium, said core and said can being composed of mild steel.
 9. The process of claim 8 wherein said chemically removing of said core and said casing is effected with an acid that is inert with respect to said titanium base metal.
 10. The process of claim 8 wherein said temperature is approximately 1,650* F. 